1. Field of the Invention
The present invention relates to the field of boat docking, and specifically concerns a modular boat lift which is supported by floating it on the water surface using side pontoons comprised of modular floats
2. Description of the Prior Art
The mooring of a boat or ship at a dock with the use of mooring lines has been known for hundreds of years. But it was not until the relatively recent past that means became available to readily raise a boat out of the water when not in use. Since the typical pleasure boat spends nearly its entire life not in use, it is highly desirable to remove the boat hull and running gear from the water whet it is not being used. This is true regardless of whether the boat is in fresh water or salt water. In fresh water algae tends to grow on the hull, while in salt water there is the growth of barnacles and other types of sea life on the hull and electrolysis often harms metal components of the boat, e.g., propellers, shafts, trim tabs, rudders and engine seals.
A great variety of devices have been employed for this purpose. One device uses davits on a dock or seawall in which books are attached to cleats on the boat and cables connected to a winch powered by electric motors that then lift the boat out of the water by brute force. It is also quite commonly known that these devices are ugly, fairly noisy, and are very dangerous if a cable parts. As a consequence, many residential communities do not permit their use.
There are a variety of patented devices that have been used to lift boats from the water. An example is Dettlang, Jr., U.S. Pat. No. 5,238,324, which teaches a combination wheeled boat dock and lift by which a boat is virtually driven around a body of water. Another example is Thomas, U.S. Pat. No. 4,686,920, which teaches a cradle type of device submerged in the water between pilings and then lifted using block and tackle powered by an electric motor. Another example is Sackett, U.S. Pat. No. 5,131,342, which discloses a shallow draft floating boat lift which employs two pontoon type flotation chambers on either side of the hull wherein lift is created using jack screws powered by electric motors.
The general concept of the use of flotation devices in combination with mechanical apparatus to achieve lifting a boat from the water, as in the present invention, is known. An example is Gates, U.S. Pat. No. 6,032,601, which also employs pontoons on either side of the boat with a cradle therebetween. However, this reference significantly differs from the present invention, in part because this reference employs pivoting arm structures and a drive mechanism that use potentially dangerous and noisy cables to raise the boat relative to the pontoons so that the hull emerges from the water. Other distinctions with this reference will become apparent upon review of the following detailed descriptions of the present invention.
Another prior art reference is Dickman, U.S. Pat. No. 5,979,349, which uses a tank with air and water levels in that tank being adjustable to raise and lower the lift. However, it also employs a dock attached jackscrew to reduce and minimize listing of the boat bull and adjusting air tube that allegedly affects listing as well.
Another approach is to employ a floating platform having a v-shape in the center thereof, a series of rollers at the bottom of the V-shape corresponding to the position of a keel on a V-hull and a winch with is capable of pulling the boat out of the water and on to the top of what amounts to a floating dock. This approach is taught by Hillman, et al, in U.S. Pat. No. 6,006,687.
Some prior art devices have used means of changing buoyancy of certain components to achieve submergence and lifting. An example of that approach is a patent issued to Siegmann, U.S. Pat. No. 6,257,159, which is an apparatus for raising and lowering boats in water that has the capability of lifting a center keel sailboat completely out of the water. It employs flotation tanks or chambers that are alternately flooded or evacuated using compressed air and which further employs an elaborate structure of eight traction mechanisms in the form of reels and apparent cables to assist in the lift effort. Siegmann represents a very complex invention.
Moody, U.S. Pat. No. 5,860,379, teaches an inflatable floating boat lift device constructed of a flexible impermeable fabric comprising main air chambers and a network of hoses and blowers which control the inflation and deflation of each main chamber independently. This device provides vertical lifting of the boat while floating on the surface of the water. The blower is operated either by 115 volt AC, or 12 or 24 volt DC power.
A further reference of interest that is somewhat older is Bradfield, U.S. Pat. No. 3,967,570, which is a floating boat dock lift that employs a variable buoyancy chamber connected to an air pump and valves. It also employs a hinged structure to the dock.
Yet another reference is that of Samoian, et al., U.S. Pat. No. 5,485,798, which discloses a floating boat lift supported by side pontoons and having a cradle lifted by the operation of hydraulic cylinders that employ water rather than hydraulic fluid, and use a parallelogram linkage in combination with the hydraulic cylinders. Samoian, et al. does not teach the modular concept or any other means to expand its boat weight handling capability.
Accordingly, what is needed is a method and apparatus to overcome some of the shortcomings and problems with the prior art. Particularly, what is needed is a boat lift with the ability to expand the size of boat lift while offering at the same time simplicity, silent operation, and low visibility of the present invention. The latter features are important because in many communities, boat lift devices are banned because of their unsightliness, potential pollution considerations, consumption of space, use of water contaminating underwater devices, noise and for numerous other reasons. Noise is a consideration because the prior art that uses buoyancy tanks does so with air pumping devices such as vacuum cleaner pumps and motors that are notoriously noisy.